Bit assembly

ABSTRACT

A cutter bit, particularly for a coal plough, is retained within a holder by a screw which passes through an aperture in the end wall of the holder.

United States Patent 1191 Ostrop Sept. 9, 1975 [54] BIT ASSEMBLY 2,l90,674 2/l940 Osgood 1, 299/93 327L080 9 1966 G l k 299 92 [75] Inventor: Berthold Ostrop, Werne, Germany owan DC I [73] Assignee: Gewerkschaft Eisenhutte Westfalia,

Westphalia, Germany FOREIGN PATENTS OR APPLICATIONS 628,458 5/1963 Belgium 1 A i 1 299/9l [22] Sept 1973 1,291,708 4/1969 Germany 299/91 [Zl] Appl. No.3 400,412

Primary Examiner-Frank L. Abbott [30] Foreign Application Priority Data Assistant Examiner-William F. Pate, Ill

Sept. 14, 1973 Germany 2244977 Attorney, Agent, or FirmThomps0n, Birch, Gauthier 52 us. (:1. i. 299/91; 37/142 A; 175/410; & Samuels 403/353 [5|] Int. Cl. E21C 15/00 [58] Field of Search 299/91-93,

299/175; 37/142 R, 142 A, 141 T; 175/413; [57] ABSTRACT 403/353 24; 85/8 A cutter bit, particularly for a coal plough, is retained within a holder by a screw which passes through an [56} References cued aperture in the end wall of the holder.

UNITED STATES PATENTS 1,595,112 8/1926 Mcntzer A. 299/91 x 4 Claims, 2 Drawing Figures Zl X 27 12 M 2 v/ PATENTEB SEP 9M5 FIG] BIT ASSEMBLY BACKGROUND OF THE INVENTION Bit assemblies for coal ploughs and the like are known which comprise a holder or housing which defines a cavity in which a root part of the bit or tool is received. The bit may have a projection which hooks into a recess in an end wall of the holder while the other end of the bit is held in place by a releasable securing device. German Pat. No. 1,291,708 discloses a bit as sembly of this type in which the bit is held in place at the other end of the holder by a lining piece which is inserted in an aperture in the wall at that end and engages between the wall and a projection on the bit and by a clamping pin which is driven through a bore in the lining piece and into a bore in the bit.

An advantage of this construction is that the securing device is readily accessible so that in theory the bit can be removed and replaced relatively easily. In practice, however, because of adverse conditions encountered in underground mining the lining piece and the clamping pin rust, especially when the plough is out of use for a prolonged time. The parts therefore become jammed and cannot be removed easily. Often, the only way of removing the jammed parts is to drill them away.

The object of this invention is to overcome this problem and provide for a bit assembly of this type a securing device which is simple to construct, easy to handle and is removable without any particular difficulty even when equipment has been left standing idle for some time.

According to the invention, the securing device takes the form of a cap screw which can be screwed through an aperture in the end wall of the holder and into a screw-threaded bore in the bit. The head of the cap screw, which is preferably cylindrical with a diameter substantially greater than that of the shank, bears against the surface of the end wall defining the aperture and retains the bit in the cavity. The screw head may be provided with a polygonal recess, more usually a hexagonal recess, to receive a suitable tool.

By making use of the invention, the bit may be re tained by a screw having a strong cylindrical head which is at least partly countersunk in the aperture in the end wall, the head of the screw acting as a projection interfitting with the wall.

Important features of the invention reside in the steps which may be taken to give the screw stability. According to one of these features, the end wall of the holder is formed with a narrow rib, ridge or shoulder which projects into the aperture and acts as a support surface for the side of the screw head. This support surface, it will be noted later, is in line with the point through which pass at least the major forces which are transmitted to the screw head from the holder or bit.

Between the head of the screw and its threaded shank, there may be interposed an enlarged unthreaded portion which bears against a support surface surrounding the mouth of the bore. To ensure that the forces applied to the screw head by the bit also pass through the aforesaid common point, this unthreaded portion may include a frusto-conical shoulder which bears against a complementary dished recess at the bore mouth. These surfaces are tightly pressed against one another when the screw is tightened so that the bore is sealed against moisture and internal rusting is prevented.

Since the forces transmitted to the screw head from the narrow shoulder and the dished recess may be arranged to intersect at a point on, or adjacent to, the screw axis, the stress suffered by the screw will be confined to the axial direction, that is, will constitute tractive stress, despite the fact that the head of the screw will be subjected to transverse loads.

The screw connection provided by the invention is particularly suited to retaining bits in bit holders such as are used in coal ploughs and other mining equipment. It can, however, also have other applications in any field in which there is desired a screw connection which will not suffer bending stress. The invention is therefore not confined to the mining field.

DESCRIPTION OF THE DRAWINGS FIG. I is a partial section taken through a bit holder showing a bit in place therein, and

FIG. 2 is an end elevation of the assembly shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a cutter bit assembly for a coal plough consists of a bit holder 10 having a cavity or compartment 12 opening towards the coal face and into which the root part of a plate-like blade part, tool or bit 11 is received. The bit holder may have a conical shank for insertion in a boring of complementary shape in the body of the plough or in a bit carrier. The bit 11 has a tip which may be made up from hard metal inserts 13.

The body of the bit holder is cut away to form a recess 15 which constitutes an extension to the compartment l2 and receives a projection 14 on the root part of the bit housed within the compartment. The projection I4 therefore hooks around the rear side of the wall I6 of the bit holder.

During assembly, the bit I1 is inserted into the com partment and the projection 14 mated with the recess 15. The bit is then pivoted around the projection (in the direction of arrow S) into the position illustrated. To permit the bit to be pivoted in this way, the wall 16 is cut away or bevelled at 17 and a slight clearance 18 is left between the opposite wall 19 and the part of the bit which lies proximate to it.

In order to retain the bit in position relative to the bit holder, the wall 19 is provided with an aperture 20 which accommodates the head 22 of a cap screw 21 which is screwed into a screw threaded bore 22' in the root part of the bit and serves to retain the latter in place within the compartment. The head 22 is cylindrical and has a hexagonal recess 23 for an appropriately shaped tool. The diameter of the head 22 is substantially greater than that of the screw shank 24 and is separated therefrom by an unthreaded portion which includes a frusto-conical section 25 and a cylindrical section 27 which has a diameter somewhat greater than the outer diameter of the threaded shank. The frustoconical section bears against a complementary surface 26 at the mouth of the bore while the cylindrical section 27 fits within a cylindrically enlarged portion of the bore. This unthreaded portion serves to seal the bore against the ingress of moisture.

As shown in FIG. 2, the aperture in the wall 19 is generally U-shaped and the circular sectioned part and parts of the tangential flat parts of the circumference of the aperture have a narrow support rib or shoulder 28 which bears against and supports the screw head over an arc of about 180.

Once the bit has been pivoted into position, the screw is inserted and tightened, whereby the bit is retained in place. When tightened, the head of the screw is situated in a partially countersunk position within the aperture 20 (it may of course, in a modification. be completely countersunk) and is supported against the frustoconical surface 26 and the narrow shoulder 28. The screw and its supporting surfaces are so dimensioned and located relative to each other that the forces acting on the screw, namely the transverse force Z transmitted to the head of the screw from the shoulder 28, the oblique forces transmitted to the screw from the surface 26 and the axial force Y, will intersect at a point M disposed substantially on the screw axis. As a result, when the bit assembly is in use, the screw is subjected to no flexural stress as a result of transverse forces.

I claim:

1. A bit assembly comprising:

a. a hollow bit holder having top and bottom walls, side walls and end walls, one of said end walls having an aperture therein communicating with the hollow interior of said holder, said bottom wall having an opening therein communicating with the hollow interior of said holder;

b. said one end wall having a shoulder formed thereon along the lower periphery of the end wall aperture;

c. an interior support member formed on the bit holder walls on the opposite side of the hollow interior of said holder from said shoulder;

d. a tool bit having a root portion inserted through the bottom wall opening into the hollow interior of said bit holder, said root portion having retaining means thereon for interacting with said bit holder support member, said root portion having an internally threaded bore which is axially aligned with the end wall aperture, said bore having its opening countersunk; and

e. a screw inserted through the end wall aperture and screwed into the bore of said root portion, said screw having a head bearing against and being supported by said one end wall shoulder, said screw having a frusto-conical surface formed between its head and threaded shank bearing against said countersunk bore opening;

f. said one end wall shoulder, said screw head, said countersunk bore opening, and said frusto-conical screw surface all being arranged relative to each other whereby forces transmitted to said screw head intersect at a point on the axis of said screw.

2. A bit assembly as claimed in claim 1, wherein said one end wall shoulder projects into the end wall aperture.

3. A bit assembly as claimed in claim 1, wherein the head of said screw is cylindrical and has a diameter sub stantially greater than that of the threaded shank of said screw.

4. A bit assembly as claimed in claim 2, wherein said one end wall shoulder engages with said screw head through an arc of about 

1. A bit assembly comprising: a. a hollow bit holder having top and bottom walls, side walls and end walls, one of said end walls having an aperture therein communicating with the hollow interior of said holder, said bottom wall having an opening therein communicating with the hollow interior of said holder; b. said one end wall having a shoulder formed thereon along the lower periphery of the end wall aperture; c. an interior support member formed on the bit holder walls on the opposite side of the hollow interior of said holder from said shoulder; d. a tool bit having a root portion inserted through the bottom wall opening into the hollow interior of said bit holder, said root portion having retaining means thereon for interacting with said bit holder support member, said root portion having an internally threaded bore which is axially aligned with the end wall aperture, said bore having its opening countersunk; and e. a screw inserted through the end wall aperture and screwed into the bore of said root portion, said screw having a head bearing against and being supported by said one end wall shoulder, said screw having a frusto-conical surface formed between its head and threaded shank bearing against said countersunk bore opening; f. said one end wall shoulder, said screw head, said countersunk bore opening, and said frusto-conical screw surface all being arranged relative to each other whereby forces transmitted to said screw head intersect at a point on the axis of said screw.
 2. A bit assembly as claimed in claim 1, wherein said one end wall shoulder projects into the end wall aperture.
 3. A bit assembly as claimed in claim 1, wherein the head of said screw is cylindrical and has a diameter substantially greater than that of the threaded shank of said screw.
 4. A bit assembly as claimed in claim 2, wherein said one end wall shoulder engages with said screw head through an arc of about 180*. 